The long-range objective of the proposed research is an understanding of mitosis in biochemical terms. We plan to study the mechanism of mitosis on three levels: 1. The biochemistry of microtubule protein and its mechanism of assembly; 2. The interactions of microtubules with isolated metaphase chromosomes; 3. The control of aster formation and the initiation of mitotic events in Xenopus oocytes and eggs as studied by microinjection. The biochemistry of microtubule assembly will be studied with purified brain microtubules using analytical ultracentrifugation and quantitative electron microscopy to characterize the nature of the depolymerization products and the pathway of tubule growth and formation. The role of GTP binding and hydrolysis, the mechanism of colchicine inhibition, and the role of phosphorylation will be studied by combining biochemical and ultrastructural analysis using purified microtubules. The mechanism by which the kinetochore nucleates assembly of microtubules will initially be studied ultrastructurally. By devising suitable biochemical methods we will then attempt to characterize the interaction biochemically. The control of aster formation will be studied using the oocyte-egg system in Xenopus. Specifically we will be concerned with the role of centrioles, and the germinal vesicle as assayed by microinjection and by their effects on microtubule polymerization in vitro.